Hollow Cathodes as an Alternative for NBI Sources: Preliminary Results on the ATHENIS Facility

Hollow cathodes (HCs) are a widely used technology in space propulsion, representing the standard for electric thrusters both as neutralizers and plasma heating sources nowadays. HC discharges have been proven to be a highly efficient and reliable plasma generation technology with demonstrated lifetimes of tens of thousands of hours without any maintenance, making these devices a valuable alternative for negative ion sources. Consorzio RFX in Padua and University of Pisa have been testing this technology on the ATHENIS facility, an innovative concept of a new neutral beam injector (NBI) source based on hall thruster designs, both in argon and with a mix of argon and hydrogen as feed gas, with plasma parameters characterized via a movable Langmuir probe. The preliminary results, described in this article, show good plasma densities (above 5 & times; 10(17) /m(3)) even at low injected powers (around 400 kW/m(3)), both in argon and with the argon-hydrogen mix. Furthermore, in the mixed fuel gas case, the Langmuir probe characteristics indicate the presence of asecond electron population, well described by a temperature similar to the accelerating potential of the HC-extracted electrons. The electron temperature remains around 2eV in all tested configurations, indicating that the radial magnetic field of the Hall thruster acted efficiently also as a magnetic filter, representing a promising feature toward negative ion production.